Although immutable trapped field Is required in superconducting bulk applications as a quasipermanent magnet, the trapped field is influenced and changed by time-varying external magnetic field in a realistic operational environment of electrical devices. This means that shielding current distribution within bulk is changed by the time-varying magnetic field and the transient magnetic flux movement results in temperature rise and finally reduction of the trapped field. In this paper, we experimentally investigated the transition of trapped field while applying external AC magnetic field with various amplitude and frequency to a disk-shaped YBCO bulk. And we also numerically investigate the relationship between characteristic of trapped-field attenuation and shielding current distribution within the bulk using a newly developed simulation program. This program is based on the finite element method (FEM) considering the voltage-current (E-J) characteristics. It is found that the shielding current distribution is dependent on frequency of AC external field and trapped field attenuation is closely related to the shielding current.
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